The present invention relates to a process for preparing discrimination criteria for identifying colors for use in a color identifying system.
Color identifying systems are adapted to identify the color of an object by measuring the intensities of different color components of the light reflected from or passing through the object and comparing the measured intensity values of the color components with a predetermined discrimination criteria. In general, three colors, i.e. red (R), green (G) and blue (B), are used as the color components. The object is irradiated with the light from a light source. To compensate for the variation of the intensity of the light from the light source, the sum S=R+G+B of the R, G and B component values are calculated, and the ratios of the components to the sum, R/S, G/S and B/S, are determined. These relative values of the color components are used as base data for identifying the color.
As to one or a plurality of colors serving as references for color identification, the above-mentioned relative values of the color components are determined. Discrimination criteria for color identification are determined with use of the relative values and are set in the system. In determining the discrimination criteria for accurate color identification, it is said to be preferable to assure at least a twofold discrimination distance. For example, when the R/S value of a color (assumed to be A color) is 50, and the R/S value of another color (B color) is 20, 50 is more than twice 20, so that there is at least a two-fold discrimination distance between A color and B color as to the R/S value. Accordingly, when a value between 50 and 20, e.g. 35, is used as a discrimination reference value, A color can be discriminated from B color with use of the R/S values, whereby accurate color identification can be accomplished.
However, when a third color (assumed.to be C color) must be identified at the same time, such a simple procedure can not be used. For example, when the R/S value of C color is 30, the discrimination distance between 50 and 30 or between 30 and 20 is not greater than two times. Although it is of course possible to identify A, B and C colors with use of the R/S values with reference to 40 which is a value between 50 and 30 and to 25 which is a value between 30 and 20, erroneous discrimination is then likely to result. In such a case, it will become necessary to utilize other components, i.e. G/S and B/S values.
Colors as small as about 3 in number can be easily identified with use of the three components of R/S, G/S and B/S with at least twofold discrimination distances assured. Nevertheless, colors as many as five colors or ten colors require considerably complicated discrimination criteria and color discriminants and yet can not always be accurately identified. Further such color discriminating criteria are greatly governed by the colors to be identified, the object, other environmental conditions, etc. and must be suitably determined by the operator for the particular color identifying system used. The criteria must be prescribed in a manual. Thus, a very cumbersome procedure is needed. Moreover, the manual needs to cover delicate conditions, such that even the slightest errors in condition setting could not infrequently influence the result of color identification greatly. Furthermore, more complicated color identifying conditions require a correspondingly longer period of time for color identification, making it difficult to achieve an increased processing speed. Even when a greater variety of color components are extracted, similar problems are inevitably encountered, and there arises a need to use a sensor of correspondingly increased size, which is objectionable.